Heretofore in commercial production there have been mainly two processes used to grind roasted coffee. The first essentially employs a Gump grinder of the type that has been traditional in the art. The second involves the use of a Nippon Crack-U-Lator of the type set forth in U.S. Pat. No. 3,190,572 issued June 22, 1965 to Gotto for Coffee Granulating Apparatus.
The first of these processes, Gump grinding, involves passing roasted coffee through fixed openings; a shearing/cutting action compresses and subdivides the beans. This generally involves employing three grinding heads, starting with a cracking head with fixed openings feeding into an adjustable grinding head and then onto an adjustable regrinding head. The key to this Gump apparatus has been the employment of cracking, grinding, and regrinding roll-pairs under conditions creating a differential in linear speed.
Nippon milling, on the other hand, typically utilizes four pairs of rolls, each pair operating at an equal rpm and linear speed, i.e., 1:1, as contrasted with the Gump. Thus, in the Nippon rolls, from the initial coarse set of rolls, the coffee is fed through a series of narrower cut rolls, all of which are similarly equipped to operate at equal rpm in each pair thereof.
In general, insofar as presently known, in the case of the Gump grinder, the cracking, grinding and regrinding sections will occur at a differential in roll speed, typically 2:1 and higher. The Nippon mill, on the other hand, wherein each of the roll pairs operate at an equal rpm, produces a cracked and granulated coffee particle having a lighter density than the Gump. The Nippon grind will generally be of a narrower particle size distribution than a Gump and have less coarse and fine particles. However, when size-reducing using the Nippon, a "silver-skin-chaff" is released in large pieces; the chaff thus produced is not broken up and this results in an unsightly product which must be separately reduced in size or removed. Furthermore, there is a reduction in the through-put of a Nippon vis-a-vis a Gump, depending upon the size of the grind; accordingly, the Nippon fine grind has less through-put than the coarser grind.
To explain further, the Nippon mill, rather than crushing or grinding, literally cracks the material into a uniform, narrow range of particle size through a series of vertical corrugated rolls. The roller surface applies a linear stress in the circumferential direction to the coffee particles being fed into it. Each peak on the rollers acts as a fulcrum point to particles bridged across the corrugation of the mating rollers. The Nippon gaps are set for each set of rolls and are locked without any give. This results in the need for a balanced staged reduction of roll pairs. As a result, the throughput is limited to the narrowest gap between the final set of rolls with the steepest pitch having the smallest clearance. The net result is a throughput which is lessened or reduced relative to the size produced. Moreover, the Nippon rolls are designed such that gravity and the angle of nip are used to limit the feed rate. On the other hand, the Gump rolls, operating at a speed differential in each pair, are designed with one of the two having lateral/horizontal cut rolls in a pair thereof to mechanically force the coffee between the rolls thereby allowing for greater throughput.
It is a primary object of this invention to increase the throughput of a grinding operation with a control of density and particle size distribution, and indeed provide an increase in capacity greater than the Nippon and the Gump as well as a significant decrease in density as desired. A second object of the invention is to meet these criteria by modifying existing equipment.